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This work presents a four-layer absorber based on graphene patterns. Periodic arrays of biased graphene nanodisks and ribbons are exploited, while a graphene sheet top layer enhances the overall absorption. The presented structure is modeled using the circuit model method and simulated to verify its validity and accuracy. A sufficient number of simulations are performed to investigate the robustness of the proposed structure versus the variation of physical parameters such as the thicknesses of the layers, the chemical potentials, and the electron relaxation time. Wideband absorption in the frequency range of 8–9.5 THz is obtained for the proposed device, which can thus be considered for use in several optical applications including optical sensing and detection. [ABSTRACT FROM AUTHOR]

Wave absorbers are considered to be fundamental building blocks for the manipulation of light. Almost all optical systems exploit absorbers to realize some functions. A highly tunable wide-band THz absorber is presented herein. Utilizing a dual-bias scheme with a single graphene layer leads to greater freedom to control the absorption response, while a conventional periodic array of graphene ribbons and a layer of graphene sheet are also exploited. Also, a circuit model representation for all the constituent parts of the proposed absorber is developed with an evolved design methodology. According to the simulation results, wide-band absorption from 3.5 to 6 THz is achieved. [ABSTRACT FROM AUTHOR]

A THz wave absorber is designed by exploiting a unique concept and method. Three layers including dielectric and graphene patterns are incorporated on top of a thick gold surface to ensure zero transmission of THz waves through the structure. A favorable dual-bias scheme is used for the periodic arrays of graphene ribbons in the first layer, while the second layer consists of periodic arrays of graphene disks. Also, a top layer consisting of a continuous graphene sheet is used to enhance the overall absorption. All the components are modeled via a circuit model approach developed based on passive circuit elements. This leads to an explicit impedance calculation for the structure, paving the way to fully predict the device behavior. By applying impedance-matching theory, the structural parameters are tuned to obtain perfect dual-band absorption at frequencies of 5.5 and 8.5 THz. Extensive simulations verify the robustness of the structure versus variations in its geometrical parameters, while a great ability to tune the absorption peaks is achieved via variation of the chemical potentials. Such robust and tunable absorbers are attractive for the design of optical sensors, detectors, and modulators. [ABSTRACT FROM AUTHOR]

A dual narrow band perfect THz absorber is presented in this work. The structure includes three layers of graphene ribbons, disks, and sheet on the TOPAS dielectric layer while a golden plate is placed at the bottom to act as a fully reflecting mirror against THz waves. According to the simulations, the device is robust enough to show independent operation versus layers thicknesses variations, chemical potentials mismatches, and changing of electron relaxation time. The designed THz absorber in this work is an appropriate basic block for several applications in THz optical systems such as sensors, detectors, and modulators. The layers in the proposed device are modeled via passive circuit elements and consequently, the equivalent circuit of the device is calculated. Leveraging developed circuit model and impedance matching concept, the proposed device is designed to perfect absorption at 1 THz and 7 THz. Ample simulations are performed using MATLAB and CST to verify the superior performance of the device. The presented manuscript considers the circuit model representation for three different layers of the device. For a unique structure, highly tunable response versus chemical potential is obtained. Circuit model approach and impedance matching theory are exploited to reduce computational time regarding conventional approaches. [ABSTRACT FROM AUTHOR]

In this study, a simple, reliable, and universal circuit model of bipolar resistive-switching random-access memory (RRAM) is presented for the circuit-level simulation of a high-density cross-point RRAM array. For higher accuracy and reliability, the compact model has been developed to match the measurement data of the fabricated RRAM devices with SiNx and HfOx switching layers showing different reset switching behaviors. In the SPICE simulation, the RRAM cross-point array is virtually realized by embedding the empirically modeled memory cells, by which device performances such as read margin and power consumption in the high-density array are closely investigated. [ABSTRACT FROM AUTHOR]

An efficient model scheme that combines the non-linear behavior of the input parasitics with the intrinsic fundamental device rate equations of the Vertical Cavity Surface Emitting Lasers (VCSELs) is proposed. A systematic methodology for the model parameter extraction from dc and ac, electrical and optical measurements, is also presented and simulation results are compared with the experimental measurements. Extraction and simulation procedures are implemented in commercial integrated circuit design tools and they are proved to be very fast while they preserve adequate accuracy. [ABSTRACT FROM AUTHOR]